Mark makes good points in his warnings. ?After spending decades as a broadcast engineer working with plate voltages between 7 and 12 KV please also follow this advice. ?Remove any watches, rings, medical alert bracelets, etc. from your person before approaching any possible live circuit voltages. ?One particular brand of FM transmitter required internal cathode/grid adjustments while in operation when installing a new final tube. ?The knobs for these controls were located less than a foot above the positive terminal of the plate supply filter capacitor inside the cabinet where the voltage was typically around 9.5 KV. ?Be safe!
toggle quoted message
Show quoted text
On Mar 15, 2024, at 17:33, Mark Davis <markad7ef@...> wrote:
?On Fri, Mar 15, 2024 at 11:14 AM, Glenn, OZ1HFT wrote:
WARNING: A tube amplifier chassis contains lethal high voltage even when unplugged--sometimes over 700 volts AC and 500 volts DC. If you have not been trained to work with high voltage then have an amp technician service your amp. Never touch the amplifier chassis with one hand while probing with the other hand because a lethal shock can run between your arms and stop your heart. Use just one hand when working on a powered amp.
One hand... Good advice... I was getting ready to post the same precaution.?
When I started working on vacuum tube electronics, I was trained to keep one hand in my back pocket. That makes it somewhat more difficult to accidentally bring your other hand into the danger zone.?
Actually, the back-pocket strategy is a good idea any time you're working on an open chassis that's connected to AC power, regardless of whether it's turned on.
Keep in mind that you don't have to be working on an amp or transmitter... 120 VAC or 90V - 150V DC in vacuum tube receiver can kill you just as dead!
There are plenty of case histories of people being maimed or killed when working on electronics on a conductive surface, and touching the table top with one hand while the other hand is touching a high-voltage source.
Another risk on older AC-powered equipment is "Hot Chassis". This occurs when the equipment is powered through an ungrounded (two conductor) AC cord, or the ground circuit is faulty when the equipment is equipped with a grounded power cord. The cause of this condition is often defective bypass capacitors from each side of the AC line to the chassis! ?When this occurs, there is 120VAC between the chassis of the affected equipment and any nearby test equipment or radio gear that is properly AC grounded.
BE CAREFUL! BE AWARE OF THE HAZARDS!
Mark - AD7EF?
